The Prince, who is working to continue the campaign made famous by Diana, Princess of Wales, spoke of one of his mother's final promises, to remember the victims of land mines.

In a passionate speech 20 years after she walked through a field of mines in one of the most famous photographs in Royal history, the Prince called for the world to become free of the weapons by 2025.

Diana, Princess of Wales, wearing protective gear, during a briefing by the British landmine-sweeping organisation Halo Trust in Huambo, central Angola, in January 1997Credit: GIOVANNI DIFFIDENTI/AFP

His speech, at Kensington Palace on International Mine Awareness Day, came as Priti Patel, International Development Secretary, announced that the government was tripling spending on landmine clearance to £100 million.

Prince Harry told an audience his mother had been "shocked and appalled by the impact that landmines were having on incredibly vulnerable people and on children in particular".

"She did not understand why more people were not willing to address the cause of so much suffering," he said.

"She refused to accept that these destructive weapons should be left where they were, just because they were perceived as too expensive and difficult to remove."

The Prince introduced to the audience two men who had met Diana as boys after they both lost legs to mines in Bosnia.

"She shared their stories with the world, and helped campaigners – many of whom are in this room – to change history," he said.

Prince Harry is patron of landmines charity the Halo Trust

"Those two young boys, Malic and Žarko, are now grown men and are with us today. 20 years on, they both still struggle with their physical and emotional injuries and with the high costs of replacing their prosthetics. "When my mother said goodbye to Žarko that August, just weeks before her untimely death, she told him he would not be forgotten.

"Please help me keep her word to Žarko and Malic, and other people like them throughout the world, who still need us to finish the job and rid the planet of landmines.

"Collectively we have the knowledge, skill, and resources to achieve it, so let's make future generations proud."

Princess Diana in Angola in 1997Credit: Anwar Hussein/Getty

Acknowledging controversy 20 years ago, he added: "At the time, the attention my mother brought to this issue wasn’t universally popular; some believed she had stepped over the line into the arena of political campaigning – but for her this wasn't about politics; it was about people."

Prince Harry has previously visited minefields in Angola and Mozambique, and is a patron of the landmines charity HALO Trust.

Credit: JOSE MANUEL RIBEIRO/Reuters

Priti Patel, the international development secretary, joined the prince to announce that the Department for International Development (Dfid) was trebling its support for landmine clearance to £100 million over three years.

In 2015 almost 5,000 people were injured and over 1,600 killed by landmines or other explosive devices left behind by conflict. More than a third were children.

Major-General James Cowan, chief executive of the HALO Trust, said the funding marked “the start of a countdown to a mine free world”.

He said: “As with the eradication of smallpox, a mine-free world is not a pipe dream but a real possibility, but only with the right financial support.”